An image re-encoding method, an image re-encoding device, and an image re-encoding program are utilized, for example in order to increase a compression ratio of image data further.
Patent literature, PTL 1, discloses an image re-encoding device in which a decoding unit decodes a source encoded stream to generate decoded video data, and at the same time, extracts an encoding parameter of the past, superimposed in the encoded stream, and a re-encoding unit receives the decoded video data and the encoding parameter of the past, and performs an encoding process using the encoding parameter of the past.
Patent literature, PTL 2, discloses a block distortion removal device in which a level difference between a target pixel and an adjoining reference pixel is calculated by a delay circuit and a subtraction unit, and inputted into a nonlinear circuit, then, the nonlinear process circuit determines that there is block distortion when the level difference is in a predetermined range, and outputs the amount of the block distortion.
Patent literature, PTL 3, discloses a decoding device, in which signal processing is performed to decrease a high-frequency component adaptively according to the difference of magnitude of a block quantization width, by supplying a control signal generated by a control signal generation unit to a variable-passband low pass filter. Here, filtering is performed: to a boundary of a unit block included in an area in which the detected block quantization width information indicates a value larger than a predetermined value, after a block quantization width detector detects the block quantization width information out of the additional information included in a bit stream; and to a boundary of a unit block included in an area in which an individually-set block quantization width value indicates a large difference from a block quantization width value set up in an adjoining area.